Filtration Constant Research Articles

Fouling mechanisms in ultrafiltration under constant flux: Effect of feed spacer design

The impact of feed spacer design on membrane fouling mechanism in ultrafiltration (UF) process under constant flux mode was systematically investigated. Thecombined intermediate pore blocking and cake filtration model was employed,coupled with experimental crossflow UF experiments of dextran and sodium alginate (SA) in aqueous feed solutions. Filtration resultsofthree different spacer geometries, which included two 3D-printed spacers based on triply periodic minimal surfaces (TPMS) (Gyroid and TCLP) and one commercial net-type spacer, were analyzed. Flux-stepping tests were performed to determine the threshold flux (TF) in each case. Experimental data were fitted using the filtration model and the results were evaluated in terms of cake filtration constant (Kc, m−1), rate of cake erosion (S, kg.m−2.s−1), particle resuspension rate (B, s−1), and specific cake resistance (α, m.kg−1), in order to understand the cake formation and erosionbehavior that is influenced by the spacer geometry. A difference in spacer performance was observed when the solute was changed from SA to dextran. The results demonstrated that spacer design has a significant effect on the fouling mechanism in UF separation. The TCLP spacer is able to operate at the intermediate pore blocking mechanism at higher fluxes compared to the net-type spacer for both solutes tested. The flow hydrodynamics induced by the spacer geometry influenced the re-suspension rate of the deposited particles in the filtration cake. Additionally, combination of spacer surface roughness and solute molecular sizes were found to be the significant factors in cake-buildup on the spacer and the membrane.

Biocarriers facilitated gravity-driven membrane filtration of domestic wastewater in cold climate: Combined effect of temperature and periodic cleaning

In this study, two lava stone biocarrier facilitated gravity-driven membrane (GDM) reactors were operated at ~8 °C and ~22 °C in parallel for treating primary wastewater effluent. Although the biocarrier reactor at 8 °C displayed less efficient removals of biodegradable organics than that at 22 °C, both GDM systems (without cleaning) showed comparable fouling resistance distribution patterns, accompanying with similar cake filtration constants and pore constriction constants by modelling simulation. Compared to the GDM at 8 °C, more foulants were accumulated on the GDM at 22 °C, but they presented similar soluble organics/inorganics contents and specific cake resistances. This indicated the cake layers at 22 °C may contain greater-sized foulants due to proliferation of both prokaryotes and eukaryotes, leading to a relatively less-porous nature. In the presence of periodic cleaning (at 50 °C), the cleaning effectiveness followed a sequence as ultrasonication-enhanced physical cleaning > two-phase flow cleaning > chemical-enhanced physical cleaning > physical cleaning, regardless of GDM operation temperature. However, significantly higher cake resistances were observed in the GDM system at 22 °C than those at 8 °C, because shear force tended to remove loosely-attached foulant layers and may compress the residual dense cake layer. The presence of periodic cleaning led to dissimilar dominant prokaryotic and eukaryotic communities in the cake layers as those without cleaning and in the lava stone biocarriers. Nevertheless, operation temperature did not influence GDM permeate quality, which met EU discharge standards.

Fouling and mitigation mechanisms during direct microfiltration and ultrafiltration of primary wastewater

Direct membrane filtration (DMF) has recently gained attention as an alternative secondary biological wastewater treatment process. This study evaluated direct microfiltration (MF) and ultrafiltration (UF) performance and cleaning protocols during crossflow DMF of primary municipal wastewater effluent. Several types of MF and UF membranes were examined by threshold flux determination, and two types of membranes (MF, 0.08 μm; UF, 100 kDa) were chosen for exploring membrane fouling mechanisms at different feed pressures via both fouling resistance analysis and optical coherence tomography (OCT) observation. The results revealed that both MF and UF displayed three-stage fouling behaviors, i.e., initial intermediate pore blocking followed by two-stage cake filtration. Increasing feed pressure from 8 kPa to 50 kPa could accelerate physically reversible fouling rate (consistent with simulated cake filtration constant). During physical flushing, the cake layer was more readily removed from the UF membrane; while residual porous cake layer was present on the MF membrane, regardless of the feed pressure. With extending filtration-cleaning cycle, shortening filtration duration and elevating cleaning solution temperature to from 25 °C to 50 °C benefited for irreversible fouling alleviation. At 50 °C, the geothermal water performed similar cleaning behaviors as clean water, facilitating lower reversible and irreversible fouling than the geothermal brine. This study shed light on the feasibility of using high temperature geothermal water for periodic physical cleaning during DMF of wastewater under Icelandic scenario.

Simultaneous determination of six main components in Bushen Huoxue prescription by HPLC-CAD

BackgroundThe Bushen Huoxue prescription is a traditional Chinese medicine formula treating diabetic retinopathy, which was developed by our research group. Catalpol, puerarin, salvianolic acid B, ginsenoside Rg1, ginsenoside Rb1 and ginsenoside Rd are six of main effective components, which could be partly representative of this prescription. The corona charged aerosol detector (corona CAD) is one kind of universal detectors equipped with the high performance liquid chromatography (HPLC). The CAD has many advantages for the analysis of complex mixtures, but too few applications in traditional Chinese medicine compounds. ObjectiveThe aims of this study are to establish a method for the determination of six components in Bushen Huoxue prescription, and to increase the use of the CAD in traditional Chinese medicine compounds. MethodsHPLC-CAD analysis was performed on an Inertsil ODS-SP (4.6 mm × 250 mm, 5 μm) with a mobile phase consisting of 0.5 % formic acid solution(A)-acetonitrile(B) at a flow rate of 1 mL/min (0−7 min, 1 % B; 7−12 min, 1 %–12 % B; 12−22 min, 12 %–19 % B; 22-40 min, 19 %–28 % B; 40−43 min, 28 %–33 % B; 43−50 min, 33 % B; 50−65 min, 33 %–42 % B). The column temperature maintained at 30 ℃, the injection volume was 20 μL, the atomization temperature mode was LOW, the filtration constant (filter) was 3.6 and data collection rate was 10 Hz. The methodology was examined and the linearity of regression of different functions was compared. Sixteen batches of samples were prepared and their contents were determined. ResultsThe six compounds showed a better linearity (R2 > 0.9990) in their concentration ranges when using the linear function. The average recoveries were 99.18 %–101.30 %. Although the RSD value of puerarin and ginsenoside Rg1 was slightly out of 3 % during the average recovery investigation, all the other methodological investigations of the six components were within 3 %. The precision, stability and repeatability of the method were good. In sixteen batches of Bushen Huoxue prescription samples, the contents of six components were 0.3138 %–0.6042 % for catalpol, 0.8095 %–1.2917 % for puerarin, 0.7416 %–1.1189 % for salvianolic acid B, 0.0231 %–0.0418 % for ginsenoside Rg1, 0.0702 %–0.1724 % for ginsenoside Rb1, 0.0384 %–0.1196 % for ginsenoside Rd. ConclusionIn this experiment, a method for the determination of six components in Bushen Huoxue prescription based on HPLC-CAD was established with high accuracy, good repeatability and simple operation, and it can provide references for the improvement of quality standard of the Bushen Huoxue prescription. It is reasonable and accessible for the CAD application in the determination of traditional Chinese medicine compound prescriptions.

Study of couple stresses and wall permeability effects on the flow in permeable membranes

This study focused on investigating wall permeability, and couple stresses effects on the fluid flow between two permeable membranes. These flows are encountered in a variety of industrial and applied biological processes, particularly in the fluid filtration process through dialyzer membranes. Darcy’s law is employed to define the fluid suction and injection via surface of the membrane. Fluid motion is assumed to be steady and Stokesian, where the flow Reynolds number is low. The exact solution for the fluid flow field is obtained in conjunction with the lubrication approximation. Explicit expressions are derived for some useful quantities of flow interest. A significant change in the flow field is noticed for the presented non-Newtonian fluid model. Graphical results show that the flow field has prominent deviations when the inlet pressure, membrane permeability, and the couple stress parameters are changed. In order to validate results, numerical values of the filtration constant and the average pressure drop for a dialyzer membrane are computed. A comparison of the derived results with existing data reveals a good agreement with experimental and empirical results. The presented results are new and can be reduced to existing results in the literature for specified values of the couple stress parameters.

Effect of a starch-based filter aid on the dewatering of fine clean coal

The dewatering of fine, flotation cleaned coals from Huaibei and Xuzhou (bituminous) and Yongcheng (anthracite) were studied. The supernatant and filter cake were examined to determine the rate and extent of flocculation and dewatering. A starch-based filter aid was used to increase flocculation and dewatering rates. The filtration constant, K, and compression index, s, of the Yongcheng slurry were measured under various conditions. A designed experiment was performed to determine optimum conditions for dewatering. The results showed that the filter aid enhanced flocculation and coagulation of the fine cleaned coal slurry, enhanced the structure of the filter cake and promoted dewatering of the cake. Moisture content in the cake was reduced to 17% after vacuum filtration.

Solid–liquid separation equipment selection and modelling

The ease with which data may be entered into, and extracted from, electronic databases using Internet based applications is providing new opportunities for understanding and modelling of complex systems. An expert system for solid–liquid separation equipment selection and elimination, using an Internet based interface coupled to such a database, is described. Also, a database containing filtration constants for a variety of different minerals is provided and an illustration of how these constants may be used in mathematical simulations of filtration processes is given. A simple experimental procedure, which can be performed using only a single test where the pressure during filtration is incrementally increased, can provide the necessary filtration constants for the simulation procedure. Hence, the database of filtration constants can be easily expanded using experimental data from this, or similar procedures. An experimental technique that measured the in situ concentration of the forming filter cake, via electrical conductivity measurements, was used to compare the simulated local cake concentrations, using the filtration constants, against the measured ones. The agreement between the simulated cake concentrations and the measured ones was excellent.

A method to investigate filtration by the use of a pressure test filter

The article describes filtration investigations on a laboratory scale by the use of a pressure test filter. It enables the estimation of filtration constants, compressibility coefficient of the final product and dewatering in a cake compression zone. A method of experimental treatment of data was proposed for particular slurries based on constants K or modified constants K′ of the characteristic filtration equation. The use of a pressure test filter makes it possible to reduce the investigation time, reduce the costs and approximate the results for other process conditions.

Cross-flow microfiltration of activated sludge using submerged membrane with air bubbling

For the purpose of developing a wastewater treatment membrane bioreactor system, cross-flow microfiltration of intermittently aerated activated sludge was carried out, as a part of the solid-liquid separation process in the bioreactor. The tubular alumina microfiltration membrane, having a pore size of 0.5 μm, was submerged in the activated sludge. A cross-flow stream over the membrane surface was produced by air bubbling, generated by a diffuser situated underneath the membrane. An exponential relationship between the steady-state flux, J ss, and the causative factors such as operating parameters and fluid characteristics was found and expressed as J ss =V L =K′u ∗1.0MLSS −0.5 , where V L, K′, u ∗ and MLSS are the lift velocity, filtration constant, air-liquid two-phase flow velocity and MLSS, respectively. The relationship, as expressed by the equation, is consistent with that for conventional cross-flow filtration using a circulation pump.

Influence of shear breakage of microbial cells on cross-flow microfiltration flux

In the cross-flow filtration of fermentation broth, cross-flow pumping applies shear stress onto bacterial cells. The resulting shear field leads to breakage of bacterial cells. In this study, the influence of cell breakage due to shear stress on filtration flux was examined. Shear stress broke baker's yeast cells and induced discharge of granulated matter such as glycogen and cell wall fragments. These smaller particles contributed to the increase of the mean specific filtration resistance. In the cross-flow filtration, cell breakage due to shear stress reduced the filtration flux because of the increase of the hydraulic resistance of the particle-packed layer, R c, which was formed on the membrane during filtration. This flux reduction was explained by considering the lift velocities, which back-transported the particles from the membrane surface. The lift velocity was expressed as follows: V L = K· u 1.0· C p −0.5· d p 0.67· η −1.0, where V L, K, u, C p, d p and η are the lift velocity, filtration constant, feed velocity, particle concentration, particle size and viscosity, respectively. In the mixture of differently sized particles such as a shear-broken cell suspension, the steady-state flux was given as a value equivalent to the smallest V L, which was derived from the calculation of the V L values for each particle representing particles grouped according to size, using the above equation.

Evaluation of Migration of Cesium-137 Adsorbed on Fine Soil Particles through Natural Aerated Soil Layer

In order to evaluate migration of 137Cs adsorbed on fine soil particles in natural aerated soil layers, filtration constants of fine soil particles between soil and pore water were determined by the inverse analysis of the results of a large scale indoor migration test (STEM) using the soil layer samples collected from the natural aerated soil layers of Tokai and Rokkasho-mura without any disturbance. The amounts of 13,Cs which migrated through the soil layer samples with the movement of fine soil particles were also determined by the inverse analysis. The filtration constant for a loamy soil layer was larger than that for a sandy soil layer and the dependence of the filtration constant on mean diameter was the same as that obtained in small scale column experiments. On the other hand, the amount of 137Cs which migrated through the soil layer sample with the movement of fine soil particles was 0.15~6.5% of introduced 137Cs and dependent on size distribution and solidification degree of the soil layer sample. Therefore, it seems that the amount of 137Cs which migrates to a long distance with the movement of fine soil particles is small in the case of a fine and solidified soil layer. A trial evaluation of the migration of 137Cs adsorbed on fine soil particles using the result of the analysis showed that the concentration decreasing effect of Rokkasho's soil layer including the loamy soil layer was larger than that of Tokai's sandy soil layer.

Evaluation of migration of cesium-137 adsorbed on fine soil particles through natural aerated soil layer.

In order to evaluate migration of 137Cs adsorbed on fine soil particles in natural aerated soil layers, filtration constants of fine soil particles between soil and pore water were determined by the inverse analysis of the results of a large scale indoor migration test (STEM) using the soil layer samples collected from the natural aerated soil layers of Tokai and Rokkasho-mura without any disturbance. The amounts of 13,Cs which migrated through the soil layer samples with the movement of fine soil particles were also determined by the inverse analysis. The filtration constant for a loamy soil layer was larger than that for a sandy soil layer and the dependence of the filtration constant on mean diameter was the same as that obtained in small scale column experiments. On the other hand, the amount of 137Cs which migrated through the soil layer sample with the movement of fine soil particles was 0.15~6.5% of introduced 137Cs and dependent on size distribution and solidification degree of the soil layer samp...

Flow of aqueous humor in the canal of Schlemm

A mathematical model is presented for the flow of aqueous humor in Schlemm's canal in the eye. The model introduces a canal segment between two collector channels as a rectangular channel with porous upper wall. Two cases have been considered in the model: (I) the inner porous wall of the canal is rigid; (II) the inner wall is collapsible. Analytical solution of the governing equation in case I is straightforward, whereas the nonlinear equation in case II is solved by an iterative procedure. Aqueous fluid pressure and flow profiles in the proposed model are drawn, and the effects of important parameters on these profiles are brought out and discussed. It is concluded that for case I, resistance to aqueous flow is influenced by the filtration constant of the trabecular and endothelial meshwork and that narrowing of the canal reduces outflow. In case II, an increase in intraocular pressure (IOP) or compliance coefficient of the canal inner wall increases the collapse of the canal, which offers increased resistance to flow resulting in the decreased flow whereas increasing filtration constant facilitates aqueous outflow. These theoretical results suggest that increased IOP or decreased rigidity of the inner wall may contribute to the development of increased resistance as observed in some cases of glaucoma and that increasing values of filtration constant may contribute to the facility of outflow increase.

An Analysis of Water Movement between Myocardial Tissue and Capillary Blood during Reactive Hyperemia

The colloid osmotic pressure (COP) of blood from the great cardiac vein was continuously measured by means of a membrane colloid osmometer during the reactive hyperemia following temporary occlusion of the anterior descending branch of the left coronary artery in anesthetized open-chest dogs. The COP increased sharply after releasing the occlusion, then decreased below the preocclusion level before gradually returning to it. These findings indicate that a measurable amount of water moved from the capillary blood into the myocardial tissues and then flowed back slowly into the capillary blood. To analyse the factors affecting this water movement, a method is proposed in which the Starling mechanism is combined with the interstitial volume elasticity and a steady-state solution of a Navier-Stokes equation. The pressure observed with a catheter wedged into a branch of the great cardiac vein was used as a measure of capillary perfusion pressure. During the coronary arterial occlusion, the filtration constant increased while the volume elasticity of the myocardial interstitial spaces decreased rapidly. The filtration constant and volume elasticity of the interstitial space under normal conditions were approximately estimated to be 2.4 X 10(-11) cm/(sec.dyn.cm-2) and 1.1 X 10(7) dyn.cm-2, respectively.

Investigations of the relations between the filtration constant of low-concentration suspensions and filtration pressure and solid-phase concentration

Investigations of the relations between the filtration constant of low-concentration suspensions and filtration pressure and solid-phase concentration

Estimation of the filtration constant of dog submaxillary gland epithelia--an approximate value of hydraulic conductivity.

To estimate the hydraulic conductivity of dog submaxillary gland, an attempt was made to determine filtration constants of the glandular epithelium by analyzing the decay curve of the stop-flow intraluminal pressure.The time course of the decay of intraluminal pressure after cessation of the secretory stimulation was found to be expressed as an algebraic sum of two exponential functions of time, one having the rapid component and the other having the slow component:P=Ae-λ1t+Be-λ2tThe rapid component is atributable to the relaxation of the myoepithelium because the rate constant of the rapid component (λ2) is in good accordance with the rate constant of the relaxation of the myoepithelium. The rate constant of the slow component (λ1) is deduced theoretically to be a product of the filtration constant and a coefficient of volume elasticity of the gland. The value of λ1, was found experimentally to be 0.00512 sec-1, and the coefficient of volume elasticity obtained by measuring the intraluminal pressure elevated by retrograde injections of fluid was 1.52 mmHg·g-gland·μl-1. From these results, the filtration constant of dog submaxillary gland was estimated to be 0.0033 μl·sec-1·mmHg-1·g-glamd-1 on the average. Recalculating the value on the basis of the surface area of the acinus per unit gland weight, a value of the filtration constant or an approximate value of the hydraulic conductivity of the acinal surface was calculated to be 0.6×10-11 cm3·sec-1·dyne-1. The numerical values of the parameters described above may be applicable under similar experimental conditions to those used in the present study.

A theoretical study on transcapillary fluid movement

The prevailing mathematical expression of the Starling hypothesis has proved to involve equivocality and inaccuracy. Assuming that transcapillary flow takes place, following Poiseuille's law, through cylindrical pores perpendicular to the internal surface of a capillary, an improved formula has been derived on the basis of the fact that driving force for filtration and resorption of fluid is equal to the algebraic sum of hydrostatic and colloid osmotic pressures at both sides of the capillary wall. The physical meaning of filtration constant, capillary filtration coefficient and mean capillary pressure are elucidated from the viewpoint of the pore theory. Discussions are given of how the rate of transcapillary fluid movement within a certain amount of a tissue must be dealt with.

Blood Flow through Capillaries with a Permeable Wall

With a view to obtaining mathematical bases for microcirculation of plasma with filtration or reabsorption the Stokes equations for steady, axisymmetric creeping flow have been applied to a Newtonian fluid flowing through a straight, uniform tube of circular section with permeable walls. As a boundary condition Starling's law is adopted, which states in mathematical version that the velocity component normal to the wall is assumed to be a linear function of the local hydrostatic pressure. It is required that if a dimensionless parameter ε=2ηκ/R (η: viscosity of the fluid, R: radius of the tube, κ: filtration constant) vanishes, the solution will be reduced to the basic Poiseuille flow with a constant pressure gradient. In fact, ε is so small that the radial component of the fluid velocity veries linearly with the axial distance, as is seen from the boundary condition. The solution of the Stokes equations to meet this requirement can be derived in a simple form.The relation between the volume flux through each section of the tube and the pressure gradient is also easily obtained. Although this solution yields a flow pattern with non-vanishing velocity component tangential to the wall, this slip flow is understood to occur in consequence of the penetration.

Mechanics of fluid movement across single capillaries in the rabbit

An analysis was made of the factors involved in the net movement of fluid through the walls of single capillaries. The method, as originally developed by Landis, utilized the movement of red blood cells in capillaries immediately after temporary occlusion with a glass microneedle as an indication of the relative predominance of either hydrostatic or colloid osmotic pressures. Comparison of transcapillary fluid movement before and after known osmotic transients with intravenous albumin made it possible to calculate the filtration constant and the net or effective driving pressure in selected capillaries. The filtration constant in the omental capillaries was lowest on the arterial side (2 to 8 × 10 −3 μ/sec) and highest on the venous side (16 to 25 × 10 −3 μ/sec). The effective hydrostatic pressure in the capillaries varied between 28−22 cm H 2O, well above the colloid osmotic pressure of the plasma proteins. The findings reaffirm the need to reconsider the precise application of the linear, constitutive relationship governing transcapillary fluid movement as postulated by Starling.

Comparison of water diffusion and water filtration across cell surfaces.

Summary.Diffusion and filtration constants for water were measured on the plasma membranes of the ovarian eggs of Rana temporaria and Danio rerio, on the body cavity eggs of Rana and Xenopus laevis, on the shed, but not developing eggs of Danio rerio, on the unfertilized and fertilized eggs of Salmo irideus and on the amoeba Chaos chaos. The filtration constant was always higher than the diffusion constant except in the trout egg where no permeability was demonstrated. The two constants varied in the same direction but far from proportionally. It is suggested that the results give information about the structure of the membranes studied.